Photographic printing papers are not required to absorb the processing liquid during development processing; therefore, attempts have been made to lower the absorption of the processing solution into the paper of the support. One method is sizing of paper to lower the absorption of a processing solution. As is well known, a conventional baryta paper has been treated by only this method. However, this method is still insufficient to lower the absorption of the processing solution.
Another method of lowering the absorption of the processing solution by a support is to coat both surfaces of a base paper with a water-resistant film such as a polyolefin. By this method, the penetration of the treating solution into the base paper is only from the cut surface at an end, but the penetration of the processing solution from the cut surface cannot be prevented completely. The treating solution, which cannot be taken off by water washing, becomes discolored by heat and the passing of time, and becomes a so-called edge contamination. This edge contamination becomes a spotted brown stain in the white portion of a photograph, and lowers the value of the photograph markedly.
The edge contamination does not appear if water washing, after development, is carried out for a long time. But this contradicts the requirement of carrying out the processing treatment within a short period of time. For this reason, it was strongly desired to lower the absorption of the processing solution from the cut surface.
It was heretofore considered to apply a sizing agent to the base paper in order to lower the absorption of the processing solution. A sizing agent like a fatty acid soap, such as sodium stearate (JP-B-47-26961) or an alkyl ketene dimer (JP-A-51-132822), and a cationic sizing agent obtained by the reaction of a carboxylic acid with a polyamine (JP-A-54-147032) have been used for supports in photographic printing papers (the term "JP-A" used herein means an unexamined published Japanese patent application, and the term "JP-B" used herein means an examined published Japanese patent application.).
However, with sizing agents of the fatty acid soap type, the absorption of the treating liquid cannot be lowered to below the present level, and it is affected by the quality of water used for the production of the base paper. When the water has a high hardness, sufficient effects cannot be obtained because of precipitate formed.
Furthermore, when an alkyl ketene dimer is used, the adhesion between the base paper and the polyolefin or a polystyrene film is poor, and to increase the adhesion, another step is required. When the cationic sizing agent, obtained by reacting a carboxylic acid with a polyamine, is used, the absorption of the processing solution may be lowered, but coloration due to the processing solution absorbed cannot be avoided.
The present inventors have made extensive investigations in order to remedy the above defect, and found that when both surfaces of a base paper, internally treated with a specified sizing agent, are coated with a polyolefin, edge contamination is markedly improved, and a photographic printing paper suitable for rapid processing can be obtained. This finding has led to the present invention.